The quality of a diamond is often mentioned in connection with its cut, color, clarity, and carat weight (the four C's). Of the Four C's (color, clarity, cut, and carat weight), cut is the least understood—and least agreed upon—aspect of diamond appearance. Current claims about the superiority of certain round brilliant diamond cuts focus mostly on three approaches:
(1) The use of specific sets of proportions (e.g., those for the AGS 0, the AGA 1A, “Class 1” cuts [as previously taught by GIA Education], the HRD “Very Good” grades, “Ideal” cuts, and “Tolkowsky” cuts);
(2) The use of viewing devices to see specific patterns or pattern elements in diamonds (e.g., FireScope™, Symmetriscope™, IdealScope, and various “Hearts-and-Arrows”—style viewers); and
(3) The use of proprietary measuring devices such as the GemEx BrillianceScope™ and ISEE2™, which measure one or more of the following aspects of diamond appearance: brilliance, fire, scintillation, and/or symmetry.
The inventors desired to begin their research on the evaluation of diamond cut with a different approach, based on the following questions: What makes a round brilliant cut (RBC) diamond look the way it does? To what degree do differences among cutting proportions create observable distinctions? Which proportion sets produce results that are deemed attractive by most experienced observers?
Early research utilizing advanced computer modeling were described briefly by Manson (1991), and then in detail by Hemphill et al. (1998) and Reinitz et al. (2001). Many other groups have used some form of computer modeling to predict appearance aspects of diamond proportion sets, including: Fey (1975), Dodson (1978, 1979), Hardy et al. (1981), Harding (1986), van Zanten (1987), Long and Steele (1988, 1999), Tognoni (1990), Strickland (1993), Shigetomi (1997), Shannon and Wilson (1999), Inoue (1999), and Sivovolenko et al. (1999). Details relating to this early work are found in the articles that are fully cited in the References section below and hereby incorporated by reference. As understood, few if any of these other studies validated their modeling results by using observation tests of actual diamonds, as is desired to do in research associated with the present invention. The validation of computer modeling by observations is deemed advantageous in the evaluation of diamond cut appearance, as without this validation there is a risk of producing results that are not applicable to the real-world assessment of diamonds.
The face-up appearance of a polished diamond is often described in terms of its brilliance (or brilliancy), fire, and scintillation (see, e.g., GIA Diamond Dictionary, 1993). Historically, however, diamond appearance has been described using other terms as well; even the addition of scintillation to this list has been a relatively recent development.
Today, while brilliance, fire, and scintillation are widely used to describe diamond appearance, the definitions of these terms found in the gemological literature vary, and there is no single generally accepted method for evaluating and/or comparing these properties in diamonds. Further, experienced members of the diamond trade use additional terms when they assess the appearance of diamonds, e.g., at various international diamond cutting centers and at trade shows, or generally by retailers and jewelry consumers. In addition to brilliance, fire, and scintillation, other words are often used such as “life”, “pop”, “lively”, “dull”, “bright”, or “dead” to describe a diamond's cut appearance. These members of the diamond trade would not generally be able to explain precisely what they mean when using such terms. In some cases, they may know whether or not they like a diamond, but may be unable to articulate exactly why.
Several existing general approaches to the question of how to fashion diamonds having the best appearance may be considered. One can start with observation comparisons such as, “diamond A looks better than diamond B”. However, without a predictive framework as to why one diamond looks better than another, such results are difficult to generalize.
Of course, tradition is another way to discover the best-looking diamond cuts: relying on historical work. However, traditional determinations of good-looking diamonds were based on that which was known at the time the historical diamond cutting styles were developed. New cutting technology makes different cuts practical, and new diamond sources yield rough with different shapes and colors. In these ways the economics and possibilities of cutting styles have changed. Unstated assumptions, such as the lower girdle facet lengths or the lighting environment in which a diamond is worn, are especially likely to change the observed quality. Thus, traditional solutions may not be the best solutions.
Another way to design or evaluate diamond cuts is to create models. Mathematical models employ optics theories to simulate how light interacts with a diamond. The properties of diamond as a material are quite well known, and calculations of the path light takes through transparent materials are not difficult, especially if computers are used to perform the necessary calculations. Prior to the widespread availability of computers, geometrical and graphical techniques were used. More recently, researchers have used computer modeling (usually ray tracing) to calculate light paths. Thus, diamond cuts and their optical properties can be modeled, to optimize a specific result, before any rough is cut. However, all models are based on assumptions, and the desired computer outcomes should be carefully defined mathematically before they can be calculated.
Predictions enable models (physical and virtual) to be checked for applicability. Predictive models can also be made physically: for instance, one can build an artificial environment for viewing diamonds. In this regard, a physically modeled viewing environment and a mathematically modeled viewing environment can be constructed and compared for agreement with one another. For any such model environment, an important question is relevance: what type of viewing environment is being modeled, and more importantly, how does the viewing environment relate to the actual environments in which the diamond will be viewed on a day-to-day basis?
Although viewing devices create a model for reality, they do not lend themselves easily to predictions. Instead, they allow qualitative methods for assessing the appearance of a diamond. Both systemization of the method and comparisons with observations made in more natural environments are needed in order to validate such devices.
Another option is the measurement of appearance aspects. For example, existing devices and systems may be used for measuring the brilliance and scintillation of a diamond. Such devices and systems tend to measure such characteristics according to some arbitrary scale, e.g., low, medium, high, and very high.
Some existing cut systems try to codify the best-looking diamonds using narrow ranges of individual proportions or ranges of combinations of a few proportions. Commonly, these systems distinguish a specific set of proportion ranges as best. In some respects, this amounts to a “bull's eye” approach: the proportion target is defined and all other proportion combinations are considered worse—progressively worse as the differential between the proportions and the target increases. This approach has a few dangers. First, these systems usually do not specify proportions for all the facets, especially for the stars, upper girdle, and lower girdle facets, which cover about 50% of a diamond's surface. Another concern is that proportions in such systems are usually specified individually, but not all combinations of acceptable proportions may lead to the same appearance or performance. Finally, there may be good looking (and well-performing) diamonds, having different proportions than the target, that can't be distinguished from bad-looking, poor-performing diamonds that are equally far away from the target. Thus, a bull's eye approach to proportions that finds some good-looking diamonds may not find them all.
Although a diamond's performance is quantifiable, “beauty” remains highly subjective. Appearance metrics are not subjective, but individual taste is. A cut system cannot guarantee that everyone prefers one set of proportions over another for all cases. Instead, as the cut grade worsens, the diamonds in each grade category change from those that everyone likes, to those that some people like, to those that nobody prefers. Indeed, research and trade interaction confirm that diamonds within a “top” grade category will be considered differently by different individuals. A grading system that fails to acknowledge differences in taste is neither scientific nor useful to the diamond trade.